Apparatus for generating wet steam having substantially constant quality



United States Patent 72] Inventors Stewart Haynes, Jr.;

Fuad T. Saadeh, Houston, Tex. [21] Appl.No. 839,101 I [22] Filed Mar. 27,1969

Division of 686,931, Nov. 30, 1967, Patent No. 3,499,488. [45] Patented Dec. 29, 1970 [73] Assignee Texaco Inc.

New York, N.Y. a corporation of Delaware [54] APPARATUS FOR GENERATING WET STEAM HAVING SUBSTANTIALLY CONSTANT QUALITY 1 Claim, 2 Drawing Figs.

[52] 11.8. CI 236/20, 122/448 [51] Int. Cl F23n 1/00 [50] Field ofSearch 236/20, 32, 33

[56] References Cited UNITED STATES PATENTS 2,387,7l7 10/1945 Clarkson 236/32 3.l93,009 7/1965 Wallace et al 166/272 3,237,692 3/ l 966 Wallace et al 166/303 Craford Controls for Steam Generators for Thermal Oil Recovery Programs" Producers Monthly. Vol. 3l, No. 5, May I967, pages 22 and 23 relied on TN 860 p. 7

Farouq Ali: Wet Steam for Thermal Recovery, Producers Monthly, Feb. 1966 (Pages 2, 4, 5, 6 and 7) TN 860 p. 7 Primary Examiner Edward J. Michael Attorneys-K. E. Kavanagh and Thomas H. Whaley ABSTRACT: An apparatus for generating wet steam of substantially constant quality wherein the heat supplied to the steam generator apparatus is controlled by means of a signal responsive to the chloride ion concentration in the liquid portion of an adiabically expanded sample of wet steam.

APPARATUS FOR GENERATING WET STEAM HAVING SUBSTANTIALLY CONSTANT QUALITY This is a division of Ser. No. 686,931, filed Nov. 30, 1967,

which matured' into US. Pat. No. 3,499,488 issued on Mar. I0, 1970.

BACKGROUND OF THE INVENTION This invention relates to an apparatus for generating wet steam of substantially constant .qualityby regulating the are the quality and enthalpy thereof. One of the common methods'for measuring such properties includes the use of a throttling calorimeter. Such a device is simple in operation. However, it applicability is limited to the range of steam qualities generally in excess of 90 percent. This limitation is due to the fact that the quality of the steam under test must be sufficiently high so that in throttling the steam expands into the superheat region. Such a device is ineffective, therefore, for measuring the quality of steam with a high liquid content as commonly encountered in oil recovery operations.

A method employing an orificemeter is sometimes used for measuring the quality of steam having a moisture content beyond the useful range of the throttling calorimeter. The orifice meter apparatus incorporates acalibrated round aperture through which steam flows at a given rate and on each side of which the pressure is measured. An empirical determination of the steam quality is made on the basis of the flow characteristics of the calibratedorifice and the measured pressures. Such a method is simple in operation and inexpensive. However, the steam quality measurements rendered therefrom are erratic and unreliable, especially when dealing with a low quality steam or a'variable steam flow rate;

Another of the methods for measuring the quality of wet steam beyond the range of the throttlingcalorimeter involves the usage of a separating calorimeter. In this method, the wet steam passes through the apparatus wherein the liquid droplets are physically separated from the vapor phase and collected. The amount of liquid thus separated over'a given period of time and knowledge of the corresponding total steam flow permit computation of the steam quality. This method can be relatively accurate providingthe liquid droplet collection is complete and thermodynamic processes that occur in the separator are well-known and under control. In

general, the steam undergoes a pressure drop in passing through the separator. This pressure drop and undetermined heat losses from the apparatus are detrimental to the accuracy of the measurements made. It is noted also that such a method requires that the entire quantity of steam produced be passed through the separating calorimeter, thereby requiring a complete diversion of the steam from its ultimate use. Since all the steam produced must be passed through the apparatus and elaborate measuring techniques must be used to determine the quality of the steam, such an apparatus does not readily lend itself to periodic quality determinations or field adaptation.

SUMMARY OF THE INVENTION This invention provides an apparatus for generating wet steam of substantially constant quality by controlling the amount of heat supplied to the steam generating apparatus by means of a signal responsive to the'chloride ion concentration which is determined in the separated liquid portion of a sam ple of the generated wet steam.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents a schematic view of the steam quality measuring apparatus in conjunction with a steam generator; and

FIG. 2 is an elevation view of the liquid-vapor separator in cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Generally, during a steam generating process, the'primary consideration is to produce steam containing the greatest amount of heattherein and with a sufficient liquid content to prohibit deposition of salts in the steam generator thereby increasing the service life of the steam generating apparatus. The quality of the produced steam is a measure of the liquid content therein while the enthalpy is a measure of the amount of heat contained therein. The quality of the steam produced is also a primary indicator of the efiiciency of the steam generator. To illustrate, when steam is used during a secondary recovery process, wherein steamtis injected into a hydrocarbon bearing formation, the effectivenessof the steam flood is determined by the amount of heat imparted by the steam to the hydrocarbons in the formation. Such a determination of the heat imparted to the underground formation is made by measuring the enthalpy of the steam injected into the formation. Further,-during the steam injection process, it is desired also to maintain and increase the service life of the steam generating apparatus. This, may be accomplished by producing a low grade steamcontaining a sufficient liquid phase to carry any foreign matter or additives that were injected into the steam generator feed water.

Feed water supplied to the steam generator has a chloride ion concentration, and hence electrical conductivity, that remains essentially constant over long periods of time. Since during the production of wet steam a fraction of the processed feed water remains liquid in the form of droplets carried with the generated steam and since these liquid droplets carry the salts and ions originally present in the feed water, the increase ofion concentrationin the liquid droplets becomes a measure of the quality of the generated steam. The steam quality X or degree of dryness, is defined as the mass fraction of dry saturated steam generatedof the total mixture and becomes, in terms of ion concentration, 1

X,=1 g, wherein'C and C represent the chloride ion concentration in the feed water and in the liquid phase of the generated steam, respectively. Alternatively, C,- and C,- may represent the conductivity of the feed water and the liquid phase of the generated steam, respectively.

When utilizing the chloride ion concentration test, the sodium chloride, in a neutral or weakly alkaline solution containing chromate, is titrated with silver nitrate. Silver chloride precipitates and at the end point red silver chromate is formed. The amount of silver chloride precipitate is then determined and becomes a measure of the sodium chloride present in the sample. Using this method, the sodium chloride concentration may be readily determined for both the feed water and the liquid droplets separated from the generated steam. It should also be noted that, a measurement of the conductivity of the feed water and a sample of liquid separated from the wet steam would provide an alternative method for determining steam quality.

In order to separate a sample of the liquid in the wet steam for the above quality determination tests, a representative sample of steam mixture is withdrawn from the steam line and expanded at constantenthalpy. Referring to FIG. 1, a sample of steam produced by the steam generating apparatus 10 is extracted from the steam conduit 11 by means of a sampling nozzle indicated at 12. The sample of steam is then expanded through the throttling tube 13, comprising a tubular orifice, at a constant enthalpy. It is noted that an expansion valve may be substituted. After this adiabatic expansion process, the expanded sample is at a pressure slightly higher than ambient atmospheric. The expanded sample of steam is then passed through a liquid-vapor separator, indicated generally at 20, wherein the liquid phase of the wet steam is coalesced at saturation conditions and collected as a representative liquid sample of the wet steam under analysis. Means are provided at 14 for measuring the temperature of the steam flowing through the steam conduit 11. It should be noted that a pressure measuring means may be substituted at 14. In the event that the steam in conduit 11 is sufficiently dry so as to result in expansion of the steam into the superheat region, the filtering elements in the liquid-vapor separator may be removed and the system used as an ordinary throttling calorimeter.

Referring to FIG. 2, the liquid-vapor separator 20 comprises a hollow cylindrical container 21 with an open top and with a tubular member 22 extending thereinto. interposed in the annular space between the container 21 and the tubular member 22 is a coalescing means 23 which is spaced from the bottom and sides of the container 21. Preferably, the coalescing means comprises a large open-pore ester base polyurethan filtering element. Alternatively, it has been found that fiber glass provides a satisfactory material from which the coalescing means 23 may be fabricated, as also would other pervious heat-resistant materials. To facilitate field usage of the equipment, the liquid-vapor separator is provided with a protective cover 24 which is attached to the cylindrical container 21 and the coalescing means 23. The expanded sample of wet steam is passed into the liquid-vapor separator 20 by means of the tubular member 22 positioned in the approximate center thereof. That part of the tubular member 22, which extends into the coalescing member 23 contains along the periphery thereof a plurality of perforations, indicated at 25, wherein the total area of these perforations is equal to or greater than the cross-sectional area of the tubular member. Steam entering through the tubular member 22 exits through the perforations 25 contained therein and then passes through the coalescing means 23 mounted about the tubular member. The coalescing means 23 contains on the top and bottom thereof, impermea ble members 26 and 27, for directing the flow of steam to exit through the sides thereof. The outer surface of the coalescing means 23 comprises a clothlike member 28 through which the exiting steam and coalesced liquid pass. A flow path for the exiting steam is provided by the annular spacing between the coalescing means 23 and the container 21, whereby the steam may exit through both the top passage between the outer cover 24 and the coalescing means 23, and through the passage between outer cover 24 and the sidewall of container 21. it should also be noted that this flow path provides insulation for the coalescing means of the apparatus. If it is desired to provide additional insulation, an insulating material, as indicated at 30, maybe used on the top and sides of the cover 24. A temperature measuring means 29, which may be either a thermometer as shown, or a thermocouple, is placed within a well projecting into the coalescing means 23 and provides a means for measuring the temperature of the fluid passing therethrough.

The inwardly tapered bottom of the container 21 provides a drain for collecting the liquid separated from the steam. The liquid is directed toward the bottom of the container 21 since the bottom of the coalescing means 23 is outwardly tapered and thereby encourages the separated liquid to flow into the bottom of container 21. After a sufficient quantity of fluid has been separated from the wet steam, the fluid sample is collected in the bottom of container 21 and evacuated therefrom by means of the elongated discharge tube indicated at 31. A discharge tube 31 is attached to the center of the container bottom and is of a configuration wherein the outlet means thereof is positioned slightly higher than the lower most portion of the container bottom. This then provides a means for accumulating a sample of the liquid separated from the wet steam required for the quality tests previously discussed. It should also be noted that the discharge tube 31 could be provided with a valve or other means for control of the flow of the collected liquid.

The liquid sample separated by means of the liquid-vapor separator 20 is then tested and compared to that of the feed water used to generate the sample of wet steam thereby allowing a determination of the quality of the sample of the wet steam.

Automatic means for regulating the quality of the steam produced b the steam generator 10 is provided by the control means 15 w ich is responsive to a signal from the quality measuring apparatus 16. The signal may be provided in a form proportionate to the desired quality minus the measured quality. The quality measuring apparatus 16 comprises a means to effect either the chloride ion concentration test or the conductivity test in conjunction with the method of the disclosure previously discussed and thereby provides a determination of the quality of the steam in conduit 11. Feed water is supplied to the steam generator 10 through a supply line 17 from the feed water tank indicated at 18. The rate of feed water supplied to the steam generator 10 is regulated by means of the valve 19 in accordance with the desired steam rate. In order to provide automatic regulation of the steam quality, control means 15, which is responsive to a signal from the quality measuring apparatus 16, regulates the heat input to the steam generator 10. This is best accomplished by regulating the air and fuel rates to the generator and thereby provides a means for controlling the quality of the steam produced by the steam generating apparatus 10.

We claim:

1. An apparatus for generating wet steam of substantially constant quality which comprises in combination:

a. a steam generating apparatus for producing wet steam comprising water vapor and unvaporized feed water;

b. means for supplying feed water containing chloride ions;

c. means for supplying heat to said steam generating apparatus;

d. means for regulating the amount of heat supplied to said generating steam apparatus;

e. means for taking a sample of produced wet steam;

f. means for expanding approximately adiabatically said sample of wet steam;

g. means for separating the portion of the liquid entrained in the expanded wet steam at approximately atmospheric pressure and at the approximately corresponding saturation temperature of said liquid;

h. means for generating a signal responsive to the concentration of chloride ions in said liquid; and

i. said means for regulating the amount of heat supplied to said steam generating apparatus being responsive to said signal, thereby regulating the quality of wet steam produced by said steam generating apparatus. 

